Hybrid bit with roller cones near the bit axis

ABSTRACT

A drill bit includes a bit body having a longitudinal axis extending there through, a plurality of journals extending downward and radially outward from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the journal axis at the base is at a first radial distance from the longitudinal axis, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body and extending axially and radially along the bit body from a first end to a second end, wherein the first end is at a second radial distance from the longitudinal axis greater than the first radial distance, and wherein the second end is at a gage region of the drill bit.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. §119, this application claims benefit of U.S. Provisional Application No. 61/898,871, filed on Nov. 1, 2013, and U.S. Provisional Application No. 61/827,978, filed on May 28, 2013, both of which are incorporated by reference in their entirety.

BACKGROUND

Historically, there have been two main types of drill bits used for drilling earth formations, drag bits and roller cone bits. The term “drag bits” refers to those rotary drill bits with no moving elements. Drag bits include those having cutting elements attached to the bit body, which predominantly cut the formation by a shearing action. Roller cone bits include one or more roller cones rotatably mounted to the bit body. These roller cones have a plurality of cutting elements attached thereto that crush, gouge, and scrape rock at the bottom of a hole being drilled.

Bit type may be selected based on the primary nature of the formation to be drilled. However, many formations have mixed characteristics (i.e., the formation may include both hard and soft zones), which may reduce the rate of penetration of a bit (or, reduces the life of a selected bit) because the selected bit is not as desirable for certain zones. For example, both milled tooth roller cone bits and PDC bits can efficiently drill soft formations, but PDC bits will often have a rate of penetration several times higher than roller cone bits.

PDC Drill Bits

Drag bits, often referred to as “fixed cutter drill bits,” include bits that have cutting elements attached to the bit body, which may be a steel bit body or a matrix bit body formed from a matrix material such as tungsten carbide surrounded by a binder material. Drag bits may generally be defined as bits that have no moving parts. However, there are different types and methods of forming drag bits that are known in the art. For example, drag bits having abrasive material, such as diamond, impregnated into the surface of the material which forms the bit body are commonly referred to as “impreg” bits. Drag bits having cutting elements made of an ultra hard cutting surface layer or “table” (often made of polycrystalline diamond material or polycrystalline boron nitride material) deposited onto or otherwise bonded to a substrate are known in the art as polycrystalline diamond compact (“PDC”) bits.

PDC bits drill soft formations easily, but they may frequently be used to drill moderately hard or abrasive formations. They cut rock formations with a shearing action using small cutters that do not penetrate deeply into the formation. Because the penetration depth is shallow, high rates of penetration are achieved through relatively high bit rotational velocities.

Roller Cone Drill Bits

Roller cone drill bits may be used to drill formations that fail more efficiently by crushing and gouging as opposed to shearing. Roller cone drill bits are also used for heterogeneous formations that initiate vibration in drag bits. Roller cone drill bits include milled tooth bits and insert bits. Milled tooth roller cone bits may be used to dill relatively soft formations, while insert roller cone bits are suitable for medium or hard formations. Roller cone drill bits include a bit body with a threaded pin formed on the upper end of the bit body for connecting to a drill string, and one or more legs extending from the lower end of the bit body. The threaded pin end is adapted for assembly onto a drill string for drilling oil wells or the like. Roller cone bits, on the other hand, may have better steerability when building curve section of a wellbore.

Hybrid Drill Bits

Both roller cone and PDC bits have their own advantages. Due to the difference in cutting mechanisms and cutting element materials, they are best suited for different drilling conditions. Roller cone bits predominantly use a crushing mechanism in drilling, which gives roller cone bits overall durability and strong cutting ability (particularly when compared to previous bit designs, including disc bits). PDC bits use a shearing mechanism for cutting, which allows higher performance in soft formation drilling than roller cone bits are able to achieve.

Thus, in drilling operations facing mixed formations, using one type of drill bit over the other may not be adequate for the entire operation. Hybrid drill bits that use a combination of one or more rolling cutters and one or more fixed blades have been proposed previously. However, problems arise during the design of these hybrid bits in trying to combine rolling cutters and fixed blades within a limited amount of space.

SUMMARY

This summary is provided to introduce a selection of concepts that are further described below in the detailed description. This summary is not intended to identify key or essential features of the claimed subject matter, nor is it intended to be used as an aid in limiting the scope of the claimed subject matter.

In one aspect, embodiments disclosed herein relate to a drill bit having a bit body with a longitudinal axis extending there through, a plurality of journals extending downward and radially outward from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the journal axis at the base is at a first radial distance from the longitudinal axis, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body and extending axially and radially along the bit body from a first end to a second end, wherein the first end is at a second radial distance from the longitudinal axis greater than the first radial distance, and wherein the second end is at a gage region of the drill bit.

In another aspect, embodiments disclosed herein relate to a drill bit having a bit body having a longitudinal axis extending there through, a bit radius measured from a gage of the bit to the longitudinal axis, at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along the gage of the bit body and a radial inward distance from the gage towards the longitudinal axis, a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements comprise a blade cutting profile, a plurality of journals extending downwardly from the bit body, a roller cone rotatably mounted to each of the journals, and a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements have a roller cone cutting profile, and wherein the roller cone cutting profile radially extends from a first end to a second end located radially inward from the gage

In yet another aspect, embodiments disclosed herein relate to a drill bit that includes a bit body having a longitudinal axis extending there through, at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along a gage of the bit body and a radial inward distance from the gage towards the longitudinal axis, at least one journal extending downwardly from the bit body, wherein the at least one journal extends a length from a base of the journal, and a roller cone rotatably mounted to the at least one journal, wherein the lowest axial point of the at least one blade is axially lower than the lowest axial point of the base of the journal.

Other aspects and advantages of the claimed subject matter will be apparent from the following description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 2 is a side view of a bit according to embodiments of the present disclosure.

FIG. 3 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 4 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 5 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 6 shows a partial view of a bit profile according to embodiments of the present disclosure.

FIG. 7 shows a model of a prior art bit.

FIG. 8 shows a model of a bit according to embodiments of the present disclosure.

FIG. 9 shows a model of the cutting pattern of a conventional bit.

FIG. 10 shows a model of the cutting pattern of a bit according to embodiments of the present disclosure.

FIG. 11 shows a graph comparing the rate of penetration of a conventional bit and a bit according to embodiments of the present disclosure.

FIG. 12 shows a graph comparing the insert scraping distance of a conventional bit and a bit according to embodiments of the present disclosure.

FIG. 13 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 14 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 15 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 16 shows a partial cross sectional view of a bit according to embodiments of the present disclosure.

FIG. 17 shows a diagram of a bit according to embodiments of the present disclosure.

FIG. 18 is a perspective view of a bit according to embodiments of the present disclosure.

FIG. 19 is a side view of a bit according to embodiments of the present disclosure.

FIG. 20 shows a partial view of a bit profile according to embodiments of the present disclosure.

FIG. 21 shows a perspective view of a bit according to embodiments of the present disclosure.

FIG. 22 shows a side view of a bit according to embodiments of the present disclosure.

FIG. 23 shows a perspective view of a bit according to embodiments of the present disclosure.

FIG. 24 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 25 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 26 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 27 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 28 shows a cutting profile of a bit according to embodiments of the present disclosure.

FIG. 29 shows a bottom view of a bit according to embodiments of the present disclosure.

FIG. 30 shows a partial schematic and partial perspective view of a bit according to embodiments of the present disclosure.

FIG. 31 shows a perspective view of a bit according to embodiments of the present disclosure.

FIG. 32 shows a bottom view of a bit according to embodiments of the present disclosure.

FIG. 33 shows a side view of a bit according to embodiments of the present disclosure.

FIG. 34 shows the cutting profile of a bit according to embodiments of the present disclosure.

FIGS. 35 and 36 show cutting simulations of a bit according to embodiments of the present disclosure.

FIG. 37 shows a bottom view of a bit according to embodiments of the present disclosure.

FIG. 38 shows a side view of a bit according to embodiments of the present disclosure.

FIG. 39 shows a perspective view of a bit according to embodiments of the present disclosure.

FIGS. 40-44 show cutting simulations of drill bits.

FIG. 45 shows a graph comparing bit simulation performance.

FIG. 46 shows a graph comparing bit simulation performance.

DETAILED DESCRIPTION

Embodiments of the present disclosure relate to hybrid drill bits having both roller cones and blades. The roller cones may be radially and/or axially offset from the blades, such that the roller cone portion of the bit mainly cuts the center of a borehole and the blade portion of the bit mainly cuts the gage portion of the borehole. For example, at least some of the cutting elements disposed on one or more blades of a bit may be positioned at gage while each of the cutting elements disposed on the one or more roller cones of the bit may be positioned a distance inward from the gage of the bit. By providing a roller cone cutting profile that is at least partially non-aligned with a blade cutting profile, the roller cone portion may maintain steerability of the bit and the blade portion may protect wear of the roller cone portion.

Blade Position Relative to Journal

According to embodiments of the present disclosure, a hybrid drill bit may include a bit body having a longitudinal axis extending there through, a plurality of journals proximate to the longitudinal axis, a roller cone rotatably mounted to each of the journals, and at least one blade protruding from the bit body and extending radially and axially along the bit body from a first end to a second end, wherein the first end is radially farther from the longitudinal axis than at least part of the at least one journal, and wherein the second end is at a gage region of the drill bit.

For example, FIGS. 1 and 2 show a top view and a side view, respectively, of a hybrid drill bit 100 according to embodiments of the present disclosure. The bit 100 has a bit body 110 with a longitudinal axis 112 extending axially there through. The bit 100 has a bit cutting face 102, a gage region 138, and a threaded pin end 104 opposite from the bit cutting face 102. The bit cutting face 102 refers to the side of the bit substantially facing in the direction of drilling, and that may engage the bottom hole of the wellbore being drilled. Drill string or other drilling tools may be attached to the threaded pin end 104 of the bit, for example, to rotate the bit 100. The gage region 138 of the bit may cut or maintain the gage, or outer diameter, of the borehole being drilled, and thus may engage a sidewall of the wellbore. Bit 100 includes a plurality of roller cones 120 and a plurality of blades 130 (though other embodiments may include one or more roller cones and/or one or more blades) arranged in such a manner that the roller cones 120 engage with and cut a bottom hole, but do not engage with the sidewall of a wellbore, and blades 130 at least engage and cut the sidewall of the wellbore. However, it is also within the scope of the present disclosure that the blades 130 may extend through the gage region 138 and into the bit cutting face 102 (thus forming a part of the bit cutting face). Because roller cones 120 engage with and cut a bottom hole (and not a side wall), the outer radial extent of the roller cones 120 is radially inside of the bit diameter, defined by at gage 138. The extent of overlap between cutting elements on roller cone 120 and blade 130 depends on the blade 130 location, relative to roller cones 120. For example, blades 130.1 (illustrated as being at offset from roller cones 120) extend to a more radially interior position than blades 130.2 (illustrated as being radially in line with roller cones 120, i.e., a radial plane of the blade overlaps roller cone).

According to some embodiments, such as shown in FIGS. 1 and 2, the bit body 110 on which the cutting face 102 is disposed is an integral, single piece body structure. The bit body 110, at the lower end of the bit (facing in the direction of cutting), may have a substantially planar or non-planar central (i.e., surrounding the longitudinal axis 112 of the bit 100) region from which journals (not shown) extend. Further, axially above the lower end of the bit 100, the bit body 110 may have a substantially cylindrical region from which blades 130 radially extend (i.e., the substantially cylindrical region does not account for the blades themselves but just considers the body structure from which the blades extend). Whether blades 130 also extend from the central region (radially interior from substantially cylindrical region) depends on the extent of blade 130 extension toward the bit center. Thus, in one or more embodiments, the radially interior portions of blades 130 may extend from the central region (radially interior from the transition of bit body 110 to being substantially cylindrical). As used herein, the terms “upper”, “uppermost” or “above” refer to the direction facing toward the threaded pin end 104 of the bit 100 and the terms “lower”, “lowest” or “below” refer to the direction facing toward the axial end of the bit having journals extending therefrom.

The bit body 110 may transition uniformly or non-uniformly from the central region to the substantially cylindrical region by a radiused, curved, angled, or other shaped transition. The size of the central region, transition, and cylindrical regions may vary. For example, a bit body may include a high slope extending from the lowest axial point of the bit towards the gage region of the bit, such as a conical or bullet shaped cutting face. Examples of bit bodies having a high slope cutting end are described in U.S. application Ser. No. 13/531,007. According to yet other embodiments, other shapes and sizes of bits and cutting tools may be used with hybrid journal and blade configurations described herein.

Referring still to FIGS. 1 and 2, roller cones 120 are each rotatably mounted to a journal (not shown) extending from the bit body 110 at the bit cutting face 102. At least one blade 130 protrudes from the bit body 110 and extends radially and axially along the bit body 110 from a first end 132 to a second end 134 (illustrated as ending at a heel surface, as that term is known in the art). As shown, the first end 132 of the blade 130.2 is positioned along the bit cutting face 102, at a radial distance 136 farther from the longitudinal axis 112 than the radially outermost portion of at least one roller cone 120 (and thus farther than the journal that the roller cone is mounted to). Depending on the size and shape of the bit cutting face 102, the blades 130 may extend a radial distance along the bit cutting face 102 as well as an axial distance from the bit cutting face 102 along a gage region 138 of the bit 100, wherein the second end 134 of the blades 130 are at the gage region 138. Further, at least one of the first ends 132 of the blades 130 and at least one of the plurality of journals may be positioned within a shared radial plane 140 (i.e., a plane intersecting the longitudinal axis 112 at a perpendicular angle), such that the axial height of the first end 132 and the axial height of the journal overlap. In other words, the radial plane 140 may intersect both the first end 132 of a blade 130 and the journal. In other embodiments, the difference in axial height between at least one journal and at least one blade first end may be large enough that no radial plane may be shared between the at least one journal and blade first end.

According to embodiments of the present disclosure, a first end of a blade may be positioned on a bit cutting face relative to at least one journal. For example, drill bits of the present disclosure may have a plurality of journals disposed at or near the longitudinal axis of the bit, wherein each journal has a journal axis extending from the base of the journal through the length of the journal. A first end of a blade may be positioned a radial distance farther from the longitudinal axis of the bit than the radial distance from the longitudinal axis to the journal axis.

For example, FIG. 3 shows a top view of a partially disassembled hybrid drill bit 300 according to embodiments of the present disclosure. The bit has a plurality of journals 320 extending from the bit body 310, wherein each journal 320 has a journal axis 322 extending from a base of the journal 320 through the length of the journal 320. As used herein, a base of a journal may be drawn along a plane intersecting the journal where it meets the bit body. For example, FIG. 20 shows a partial view of the profile of a bit 180 having a plurality of blades and a journal 190 extending from a bit body 195. The journal 190 has a journal axis 192 extending from a base 194 of the journal 190 through the length of the journal 190. The base 194 of the journal 190 is shown by a plane intersecting the journal 190 where it extends from the bit body 195.

Referring again to FIG. 3, the journals 320 are positioned at the bit cutting face such that each of the journal axes 322 are at a first radial distance 325 (at the intersection of the journal axis 322 with the bit body 310) from the longitudinal axis 312 of the bit 300. As used herein, the term “first radial distance” refers to the radial distance measured between the longitudinal axis of a bit and the journal axis of a journal at its base. As shown, the bit 300 has three journals 320 with journal axes 322 at the same first radial distance 325. However, in other embodiments, a hybrid drill bit may have more or less than three journals, as well as non-equal first radial distances. For example, as shown in FIGS. 18-20, a hybrid drill bit may have one journal with a roller cone rotatably mounted thereto, and as shown in FIGS. 21-23, a hybrid drill bit may have two journals with a roller cone rotatably mounted thereto. Further, in embodiments having more than one journal, each axis of the journals may be at an equal radial distance from the bit longitudinal axis, or each axis of the journals may be at different radial distances from the bit longitudinal axis. According to embodiments of the present disclosure, a first radial distance may range from a lower limit of 0, greater than 0, 1/32, 1/16, ⅛ or ¼ of the bit radius to an upper limit of ⅛, ¼, ⅓, or ½ of the bit radius, wherein any lower limit may be combined with any upper limit. For example, in some embodiments, a first radial distance may range from between 0 and ½ of the bit radius (radial distance from the bit longitudinal axis to the bit gage). In some embodiments, a first radial distance may range from less than ⅓ of the radial distance to the bit gage. In some embodiments, the first radial distance may range from less than ¼ of the radial distance to the bit gage. In some embodiments, the first radial distance may be zero, i.e., at the bit longitudinal axis.

Additionally, a plurality of blades 330 extend radially from the bit body 310. Each of the blades 330 extends axially along the bit body 310 from a first end 332 (positioned at the bit cutting face such that the cutting elements thereon may cut and engage a wellbore bottom hole) to a second end 334 (at a gage region of the bit such that the cutting elements thereof may cut and engage a side wall of the wellbore). Further, blades 330 may have a top face 337 (which faces radially outward from the bit body), a leading face 336 (which faces in the direction of bit rotation), and a trailing face 338 opposite from the leading face 336. The first end 332 of a blade 330 may be a wall that is radiused or otherwise transitioned from the base of the blade (at the bit body) to the top face 335. For example, a first end 332 may include a sloped, curved, or substantially perpendicular wall extending from the bit body to the top face 335 of the blade 330. The first end 332 of each blade 330 is at a second radial distance 335 from the longitudinal axis 312 (measured from the longitudinal axis 312 to the base of the first end 332). As shown, the first end 332 of each blade 330 is at an equal second radial distance 335 from the longitudinal axis 312. However, in some embodiments, the first ends of a plurality of blades may be at different radial distances from the longitudinal axis (for example, as illustrated in FIG. 1, where blades 130 aligned with the roller cones 120 have a larger second radial distance than blades 130 located between adjacent roller cones 120). In some embodiments, hybrid bits having two journals may have blades at a second radial distance proximate to the first radial distance due to larger room between roller cones.

According to embodiments of the present disclosure, a second radial distance may range between ¼ and ½ of the bit radius from the longitudinal axis. In some embodiments, a second radial distance may range from greater than ¼ of the radial distance to the bit gage from the longitudinal axis. In some embodiments, a second radial distance may range from greater than ⅓ of the radial distance to the bit gage from the longitudinal axis. In some embodiments, a second radial distance may range from greater than ½ of the radial distance to the bit gage from the longitudinal axis. Further, in some embodiments, a second radial distance may range from greater than ⅔ of the radial distance to the bit gage from the longitudinal axis. The second radial distance may be designed based on the first radial distance to provide an overlapping journal/blade profile in the radial direction. In such embodiments, in addition to the first and second radial distances, the journal size and angle of journal extension may also be adjusted such that the radial distance from the bit longitudinal axis to the radially outermost point of the journal is larger than the second radial distance.

The first end of a blade may be positioned at a second radial distance (measured from the bit longitudinal axis to the base of the first end) that is greater than a first radial distance measured from the bit longitudinal axis to a journal axis at the base of the journal. For example, in embodiments having more than one journal equally spaced from the bit longitudinal axis and more than one blade equally spaced from the bit longitudinal axis, such as shown in FIG. 3, the second radial distance measured between the bit longitudinal axis and the first end of each blade is greater than the first radial distance measured between the bit longitudinal axis and each journal axis at the base of the journal. According to some embodiments having more than one journal and more than one blade, two or more of the second radial distances (measured to the first end of blades) may be different and/or two or more of the first radial distances (measured to the journal axes) may be different, wherein each of the second radial distances are greater than the first radial distances. For example, a bit may have a first blade positioned at a second radial distance (measured between the bit longitudinal axis and the first end of the first blade) that is greater than a second radial distance measured to the first end of a second blade, and a first journal is positioned at a first radial distance (measured between the bit longitudinal axis and the journal axis of the journal at its base) that is greater than a first radial distance measured to a journal axis of a second journal, wherein each of the second radial distances are greater than each of the first radial distances.

In some embodiments, a bit may have at least one second radial distance (measured from the bit longitudinal axis to the first end of a blade) that is greater than a first radial distance (measured from the bit longitudinal axis to a journal axis of a journal at its base) and at least one second radial distance (measured from the bit longitudinal axis to the first end of a blade) that is less than the first radial distance. For example, a bit may have two blades positioned at different second radial distances, wherein one of the blades is at a second radial distance greater than a first radial distance measured between the bit longitudinal axis and a journal axis, and wherein the other of the blades is at a second radial distance less than the first radial distance. Other embodiments may have other hybrid blade and journal configurations, wherein at least one second radial distance measured to a blade is greater than at least one first radial distance measured to a journal axis.

As discussed above, a roller cone may be rotatably mounted to journals extending from a bit body. Roller cones may include bodies having rounded, conical, or disc shape and a plurality of cutting elements disposed thereon. For example, referring again to FIG. 1, a roller cone 120 has a frustoconical shaped body with a plurality of cutting elements 125 disposed thereon. Roller cone sizes may differ with respect to one or more of a roller cone's outer radius, nose projection, radius of curvature, etc. As shown, the roller cone 120 has three circumferential rows of cutting elements 125. However, other embodiments may have more or less than three rows of cutting elements. Further, roller cones may have cutting elements disposed thereon in arrangements other than in rows.

Roller cones may be rotatably mounted to a journal using a retention system, such as a roller bearing retention system, a ball bearing retention system, or other retention method known in the art. For example, a roller cone may be rotatably mounted to a journal on a bit of the present disclosure using a ball bearing retention system such as described in U.S. Publication No. 2011/0162893, as described in U.S. Publication No. 2011/0024197, or as described in U.S. Publication No. 2011/0023663.

Further, journals may extend from a bit body at different angles with respect to the longitudinal axis of the bit. For example, referring now to FIG. 16, a partial cross sectional view of a bit 600 is shown. The bit 600 has a longitudinal axis 612 extending axially through the bit 600 and a journal 620 extending downwardly (in a direction toward the cutting direction) and radially outwardly from the bit body 600, such that a journal axis 622 extending through the length of the journal 620 forms an angle 630 with the longitudinal axis 612 of the bit 600. The angle 630 formed between the intersection of the longitudinal axis 612 and the journal axis 622 may be an acute angle and may range from greater than 0 degrees to less than 90 degrees. In some embodiments, a journal axis may be parallel with the longitudinal axis. While FIG. 16 shows the angle 630 for a single journal, one skilled in the art should appreciate, that each journal may form an acute angle with respect to the longitudinal axis of the bit, which may be the same or different from the other journals.

According to embodiments of the present disclosure, journals may extend from different axial locations of a bit body or may extend from the same axial locations. For example, the axial locations of journal axes for two or more journals at the journals' bases (point 625 in FIG. 16) may be separated by an axial distance. The axial distance measured between two journals may vary depending on the size and shape of the bit body, and may range, for example, from greater than zero to less than half of the journal length. For example, in embodiments having different cone sizes, the journals may have an axial separation ranging from 0 to 1 inches (25 mm). In some embodiments, two or more journals may be positioned at the same axial location.

In some embodiments, the journals (and roller cones 720) may be provided with an offset, as shown in FIG. 17. Journal/roller cone offset may be determined by viewing the drill bit from the bit cutting face on a horizontal plane that is perpendicular to the longitudinal axis 712. Offset, represented as 721, is the angle between a journal axis 722 and a line 723 on the horizontal plane that intersects the longitudinal axis 712 and the nose 724 of the roller cone 720. A positive offset is defined by an angle opening with the direction of rotation 715 of the drill bit 700. A negative offset is defined by an angle against the direction of rotation 715 of the drill bit. As shown in FIG. 17, a positive offset is provided for each roller cone 720; however, in other embodiments, any combination of positive and/or negative offsets or solely negative offsets may be used. In a particular embodiment, any number of roller cones (one or more or all) may be provided with zero or no offset, different offset directions and/or different magnitudes of offset. For example, in embodiments where one roller cone is larger than the others, it may be desirable for that roller cone to at least have a different magnitude of offset.

Additionally, roller cone offset may be used alone or in combination with varying roller cone separation angles 726. Specifically, when a journal axis is offset or skewed with respect to the longitudinal axis of the bit, the roller cone separation angle 726 may be determined by the angle formed between two lines 723 on the horizontal plane that intersects the longitudinal axis 712 and the nose 724 of roller cone 720. For example, the bit 700 shown in FIG. 17 has three cones 720, each having a cone separation angle 726 of 120° (angle between pairs of neighboring journal axis 721 (or 723) when projected upon a horizontal plane that is perpendicular to the longitudinal axis 712 of the drill bit 700. However, in other embodiments the separation angles between neighboring journals/roller cones may not be uniform. Further, one skilled in the art should appreciate that the present disclosure is not limited to bits having three roller cones, but equally applies to bits having any number of multiple cones, including for example, two or four roller cones. The separation angle between roller cones may depend, in some part, on the number of roller cones on a bit, but may also depend on other desired roller cone separation angle variances and if a blade is disposed between the roller cones.

According to embodiments of the present disclosure, the first end of a blade may be positioned on a bit cutting face at a radial distance farther from the bit longitudinal axis than the axis of a journal at its base, wherein the first end of the blade radially overlaps with a portion of the journal. For example, in some embodiments, at least one journal may be positioned on a bit cutting face such that the journal axis is at a first radial distance from the bit longitudinal axis and at least one blade has a first end positioned at a second radial distance from the longitudinal axis that is greater than the first radial distance but less than the radial distance from the bit longitudinal axis to the radially outermost point of the journal.

For example, FIG. 5 shows a cutting profile 500 of a hybrid drill bit according to embodiments of the present disclosure. The hybrid drill bit may include two journals and four blades, wherein each journal has a roller cone rotatably mounted thereon. The cutting profile 500 shows the profile of the two journals 510, the roller cones 520, the cutting elements 521 disposed on the roller cones 520, and the cutting elements 531 disposed on blades (not shown). The journals 510 have journal axes 512, wherein the base of the journal axes 512 are at a first radial distance 515 from the longitudinal axis 505. The first ends of the blades (not shown) on which cutting elements 531 are disposed are at a second radial distance 535 that is greater than the first radial distance 515 but less than the radial distance 517 from the bit longitudinal axis 505 to the radially outermost point 518 of the journals 510. In the embodiment shown, the radially most inward blade cutting element (which may also be referred to as the first blade cutting element) 532 is positioned proximate to the first end of the blade such that the first blade cutting element 532 is at a radial distance greater than the first radial distance 515 but less than the radial distance 517 from the bit longitudinal axis 505 to the radially outermost point 518 of the journals 510. Further, as shown, the second radial distance 535 is less than the radial distance 527 from the bit longitudinal axis 505 to the radially outermost point 528 of the roller cone 520 profile.

According to embodiments of the present disclosure, the radial distance from the bit longitudinal axis to the radially outermost point of a journal may overlap with the radial distance from the bit gage to the first end of a blade, such that the radial distance from the bit longitudinal axis to the radially outermost point of the journal extends at least to the radius of a first blade cutting element (i.e., a cutting element positioned closest to the first end of the blade). In some embodiments, the radial distance from the bit longitudinal axis to the radially outermost point of a journal may extend past at least ¾ of a first blade cutting element in a blade cutting profile. In some embodiments, the radial distance from the bit longitudinal axis to the radially outermost point of a journal may extend to at least the entire diameter of a first blade cutting element in a blade cutting profile. For example, as shown in FIG. 5, the radial distance 517 from the bit longitudinal axis 505 to the radially outermost point 518 of a journal 510 extends past the diameter of the first blade cutting element 532 in the blade cutting profile 531, and past the second and third blade cutting elements. In some embodiments, the radial distance from the bit longitudinal axis to the radially outermost point of a journal may extend past more that the first three blade cutting elements along the blade cutting profile (i.e., past the three blade cutting element positions radially closest to the bit longitudinal axis), for example, past four blade cutting elements, past five blade cutting elements, or more. In embodiments having the radial distance from the bit longitudinal axis to the radially outermost point of a journal extend radially past at least a portion of a first cutting element of a blade cutting profile, a portion of the roller cone cutting profile overlaps with a portion of the blade cutting profile, such that at least one roller cone cutting element and at least one blade cutting element has shared cutting duties (i.e., may both cut along a shared radial path). In other words, in embodiments having a portion of the roller cone cutting profile overlap with a portion of the blade cutting profile, the radially outermost roller cone cutting elements may have shared cutting duties with the radially innermost blade cutting elements. The number of roller cone cutting elements and blade cutting elements having shared cutting duties may depend on how much radial overlap the roller cone cutting profile and blade cutting profile have.

Radial Positions

Referring again to FIGS. 1 and 2, a plurality of blade cutting elements 135 are disposed on each blade 130, and a plurality of roller cone cutting elements 125 are disposed on each roller cone 120. As shown, the blade cutting elements 135 have planar cutting faces, while the roller cone cutting elements 125 have non-planar cutting faces 125. However, different types of cutting elements may be used on the blades 130 and roller cones 120. For example, as shown in FIG. 15 (which is discussed below), both blade cutting elements and roller cone cutting elements may have planar cutting faces. Cutting elements used with hybrid drill bits of the present disclosure may include polycrystalline diamond compacts (PDCs), diamond grit impregnated inserts (“grit hot-pressed inserts” (GHIs), natural diamond, milled steel teeth, tungsten carbide inserts (TCIs), diamond enhanced inserts (DEIs), or conical shaped (or other substantially pointed) cutting elements.

The blade cutting elements 135 form a blade cutting profile, and the roller cone cutting elements 125 form a roller cone cutting profile. As used herein, a cutting profile (e.g., a blade cutting profile and a roller cone cutting profile) refers to the profile or outline of cutting elements as they would appear in rotated view, i.e., when the bit rotated about its longitudinal axis and the roller cones are rotated about their rotational axes. For example, FIG. 4 shows a cutting profile 400 of a hybrid drill bit according to embodiments of the present disclosure. The cutting profile 400 includes a blade cutting profile 430 and a roller cone cutting profile 420. The roller cone cutting profile 420 may extend a radial distance 426 from the longitudinal axis 412 of the hybrid drill bit or a point near the longitudinal axis to an outer diameter 427 of the roller cone cutting profile 420, and the blade cutting profile 430 may extend a radial distance 436 from an inner diameter 435 of the blade cutting profile 430 to an outer diameter 437 of the blade cutting profile 430. According to embodiments of the present disclosure, the outer diameter 437 of the blade cutting profile 430 may be at the gage of the bit. The roller cone cutting profile 420 may radially overlap with the blade cutting profile 430 within the radial extent of a first row 422 of roller cone cutting elements (i.e., the row of cutting elements positioned farthest from the roller cone base). In some embodiments, the roller cone cutting profile 420 may radially overlap with the blade cutting profile within a distance 446, which may be equal to sin(journal angle)×(diameter of the first row). That is, the overlap may range from within the end points of that distance 446. For example, a roller cone cutting profile may radially overlap with the blade cutting profile a distance ranging from less than 0.1 inches (2.5 mm) in some embodiments and less than 1.5 inches (38.1 mm) in some embodiments. According to some embodiments of the present disclosure, the roller cone cutting profile may not radially overlap the blade cutting profile. In such embodiments, the roller cone cutting profile may be radially adjacent to the blade cutting profile, or the roller cone cutting profile may be located a radial distance apart from the blade cutting profile. In other embodiments, the blade cutting profile may overlap with the first row cutting element profile of the roller cone cutting profile. Further, in one or more embodiments, the blade cutting profile may overlap with the first row cutting element profile, but when considering the roller cone cutting elements that are engaging with the bottom hole, there is no overlap. That is, the overlap is with cutting elements that are rotated in an off-bottom position. However, in one or more other embodiments, the blade cutting profile may overlap with roller cone elements that are rotated in an on-bottom position.

Further, in one or more embodiments, the blade cutting profile may form at least a gage region of the bit, and may extend radially inward into what would be considered a shoulder region (as that term is used in conventional fixed cutter bits), as illustrated in FIG. 4, for example. That is, each blade cutting element is at an axially lower position relative to the radially outer “adjacent” (when viewed in a rotated profile view) blade cutting element. Further, depending on the shape and curvature of blades (and location of cutting elements), the axially lowermost blade cutting element may not be the radially most interior blade cutting element, as illustrated in FIG. 5, for example. In such an embodiment, the blade cutting profile extends through the shoulder, into what would be considered a nose region.

According to some embodiments, a roller cone cutting profile may radially overlap with the blade cutting profile a distance ranging less than ½ of the bit radius. For example, FIG. 24 shows a cutting profile 2400 of a hybrid drill bit according to embodiments of the present disclosure. The cutting profile 2400 includes a blade cutting profile 2430 and a roller cone cutting profile 2420. The roller cone cutting profile 2420 may extend a radial distance 2426 from the longitudinal axis 2412 of the hybrid drill bit or a point near the longitudinal axis 2412 to an outer diameter 2427 of the roller cone cutting profile 2420, wherein the outer diameter 2427 of the roller cone cutting profile 2420 is a distance inward from the bit gage 2437. The blade cutting profile 2430 may extend a radial inward distance 2436 from the gage 2437 of the bit to an inner diameter 2435 of the blade cutting profile 2430. The radial distance 2426 of the roller cone cutting profile 2420 may radially overlap with the radial inward distance 2436 of the blade cutting profile 2430 a distance 2446 ranging up to ½ of the bit radius (wherein the bit radius is measured from the longitudinal axis to the bit gage). Further, as shown in FIG. 24, the radially most inward blade cutting element (at distance 2435) overlaps with a roller cone cutting element disposed on the first row rotated in an on-bottom position.

Referring again to FIG. 4, a center cutting element 460 may be positioned at or near the longitudinal axis 412 on the bit cutting face. The roller cone cutting profile 420 may extend from proximate the cutting element 460 to the blade cutting profile 430, such that the cutting profile of the bit cutting face includes (from the longitudinal axis to the bit gage) a center cutting element 460 profile, the roller cone cutting profile 420, and the blade cutting profile 430. In such embodiments, the roller cone cutting profile 420 may extend from a distance away from the longitudinal axis 412 to an outer diameter 427. A center cutting element may be used in combination with other bits according to embodiments of the present disclosure having more than one roller cone and at least one blade, wherein the center cutting element is positioned at or near the bit longitudinal axis and radially inward from the roller cones. For example, the embodiments shown in FIGS. 13-15 include a center cutting element positioned at and extending along the longitudinal axis of the bit. The embodiment shown in FIG. 23 also includes a center cutting element positioned at or near the bit longitudinal axis, wherein the center cutting element extends substantially parallel with the longitudinal axis. In some embodiments, a bit may not include a center cutting element, wherein the cutting profile of the bit cutting face includes the roller cone cutting profile extending from at or near the longitudinal axis to an outer diameter and the blade cutting profile extending from the bit gage radially inward to at least the outer diameter of the roller cone cutting profile. For example, FIG. 5 shows a cutting profile of a bit having no center cutting element, wherein the cutting profile 500 includes the roller cone cutting profile 520 extending from at or near the longitudinal axis 505 to an outer diameter (radially inside of bit gage) and the blade cutting profile 530 extending to the bit gage.

According to embodiments of the present disclosure, a drill bit may include a bit body having a longitudinal axis extending there through, a bit radius measured from a gage of the bit to the longitudinal axis, at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along the gage of the bit body and a radial inward distance from the gage towards the longitudinal axis, a plurality of journals extending downwardly from the bit body, and a roller cone rotatably mounted to each of the journals, wherein the radial inward distance ranges from ⅓ to ¾ of the bit radius.

For example, FIG. 26 shows a cutting profile 2600 of a bit according to embodiments of the present disclosure, wherein the bit has at least one blade (represented by the blade cutting profile 2630) extending an axial distance along the gage 2637 of the bit body and a radial inward distance 2636 from the gage 2637 towards the longitudinal axis 2602, a plurality of journals 2610 extending downwardly from the bit body, and a roller cone (represented by the roller cone cutting profile 2620) rotatably mounted to each of the journals. The bit radius 2605 is measured from the gage 2637 of the bit to the longitudinal axis 2602 of the bit. According to embodiments of the present disclosure, the radial inward distance 2636 of the blade cutting profile 2630 may range from a lower limit of ⅓, ½ and ¾ to an upper limit of ½, ¾ and ⅘ of the bit radius 2605, wherein any lower limit may be used in combination with any upper limit.

According to embodiments of the present disclosure, a drill bit may include a bit body having a longitudinal axis extending there through, at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along a gage of the bit body and a radial inward distance from the gage towards the longitudinal axis, a plurality of blade cutting elements disposed on the at least one blade and forming a blade cutting profile, at least one journal extending downwardly from the bit body, a roller cone rotatably mounted to the at least one journal, and a plurality of roller cone cutting elements disposed on each roller cone and forming a roller cone cutting profile, wherein the roller cone cutting profile radially extends from a first end to a second end located a radial distance inward from the gage, and wherein the blade cutting profile radially overlaps with the roller cone cutting profile.

For example, FIGS. 32 and 33 show a bottom view and a side view of a drill bit 3200 having a bit body 3201, a longitudinal axis 3202 extending through the bit body 3201, at least one blade 3210 protruding from the bit body, wherein the at least one blade 3210 extends an axial distance along a gage 3204 of the bit body and a radial inward distance from the gage towards the longitudinal axis 3202, a plurality of blade cutting elements 3212 disposed on the blades 3210 and forming a blade cutting profile, at least one journal (shown in FIG. 34 as 3230) extending downwardly from the bit body 3201, a roller cone 3220 rotatably mounted to each journal, and a plurality of roller cone cutting elements 3222 disposed on each roller cone 3220 and forming a roller cone cutting profile. As shown, the roller cones 3220 and roller cone cutting elements 3222 disposed thereon do not extend to the gage 3204 of the bit 3200.

FIG. 34 shows a rotated cutting profile view of the bit 3200 shown in FIGS. 32 and 33. As shown, the roller cone cutting elements 3222 disposed on the roller cones 3220 form a roller cone cutting profile 3224, and the blade cutting elements 3212 form a blade cutting profile 3214. The roller cone cutting profile 3224 may extend a radial distance from a point near the longitudinal axis 3202 to an outer diameter 3227 of the roller cone cutting profile 3224, wherein the outer diameter 3227 of the roller cone cutting profile 3224 is a distance inward from the bit gage 3204. The blade cutting profile 3214 may extend a radial inward distance from the gage 3204 of the bit to an inner diameter 3215 of the blade cutting profile 3214. The radial distance of the roller cone cutting profile 3224 may radially overlap with the radial inward distance of the blade cutting profile 3214 a distance ranging up to ¾ of the bit radius (wherein the bit radius is measured from the longitudinal axis to the bit gage).

Further, as shown in FIG. 34, a plurality of the roller cone cutting elements 3222 along the on-bottom position may radially overlap with a plurality of blade cutting elements 3212 along the on-bottom position. As used herein, an on-bottom position may refer to the position at which cutting elements contact or extend in the direction towards the bottom, or axially lowest part, of the wellbore. In cases of directional drilling, an on-bottom position may refer to the position at which cutting elements contact or extend towards a formation face in the direction of drilling. As shown, the roller cone cutting profile 3224 along the on-bottom position radially extends from a first end 3226 to a second end 3228, wherein the second end 3228 is located a radial distance inward from the gage 3204 and a radial distance inward from the roller cone outer diameter 3227. The blade cutting profile 3214 along the on-bottom position extends a radial inward distance overlapping with the roller cone cutting profile 3224 along the on-bottom position, wherein the on-bottom radially overlapping distance 3240 may range from greater than the radius of a blade cutting element and/or roller cone cutting element to less than ¾ of the bit radius. In some embodiments, an on-bottom radially overlapping distance between a roller cone cutting profile and a blade cutting profile may range from greater than ¼ of the bit radius. In some embodiments, an on-bottom radially overlapping distance between a roller cone cutting profile and a blade cutting profile may range from ½ to ¾ of the bit radius.

Referring still to FIG. 34, the roller cones 3220 may have an extension length 3221 and a diameter 3223, wherein the diameter 3223 decreases from the roller cone base along the extension length 3221. As shown, the roller cones 3220 may have an extension length 3221 that is equal to or greater than the largest diameter 3223 along the extension length 3221. According to embodiments of the present disclosure, roller cones may have an extension length to diameter ratio ranging from 0.5 to 2, wherein the extension length is measured from the base of the roller cone to the apex (opposite the base) of the roller cone, and wherein the diameter is measured along the widest portion of the extension length. In some embodiments, such as the one shown in FIGS. 32-34, the extension length to diameter ratio may range from about 0.7 to 1.1. In some embodiments, such as the one shown in FIG. 5, the extension length to diameter ratio may range from about 0.5 to 0.8. Further, in embodiments using roller cones with a larger extension length to diameter ratio, the roller cone may extend to near or overlap with the nose region of a blade. As used herein, a nose region of a blade may refer to the region around the point along a convex region of the blade profile in rotated profile view at which the slope of a tangent to the blade profile is zero. For example, as shown in FIG. 34, the roller cone 3220 extends radially past (and overlaps with) the nose region 3216 of the blade cutting profile 3214.

Using roller cones with a larger extension length to diameter ratio may allow for greater cutting profile overlap. For example, according to embodiments of the present disclosure, a blade cutting profile may radially overlap with a roller cone cutting profile up to the entire radial length of the roller cone cutting profile. In some embodiments, a blade cutting profile may radially overlap with a roller cone cutting profile ranging from a lower limit of ⅛, ¼, ⅓ or ½ of the roller cone extension length to an upper limit of ¼ ⅓, ¼, ⅔, ¾ or 9/10 of the roller cone extension length, wherein any lower limit can be used in combination with any upper limit. Further, a blade cutting profile may radially overlap with a roller cone up to the entire roller cone extension length. For example, in some embodiments, a hybrid bit may include a roller cone mounted to a journal positioned at a journal angle of 0 degrees and at least one blade extending axially along the bit gage and a distance radially inward from the bit gage, wherein the roller cone has an extension length less than the bit radius (such that the roller cone does not extend to the gage of the bit), and wherein the radial inward distance of the blade overlaps the entire roller cone extension length.

FIGS. 35 and 36 show drilling models from a hybrid bit according to embodiments of the present disclosure having extended length roller cones, such as shown in FIG. 34, wherein the roller cone cutting profile overlaps with the blade cutting profile. As shown in FIGS. 35 and 36, the simulated blade cutting profile 3510 cuts along the outer diameter 3520, or sidewall, of the borehole and along the bottom face 3525 of the borehole, and the simulated roller cones 3530 of the bit cut along the bottom face 3525 of the borehole but do not extend to the outer diameter 3520 of the borehole. Indenting and gouging cutting action is simulated from the roller cone cutting profile, while scraping cutting action is simulated from the blade cutting profile. FIG. 36 shows the simulated cutting action, wherein mixed indenting and scraping occur in the overlapping region of the roller cone cutting profile and the blade cutting profile resulting from simulated joint roller cone cutting action and blade cutting action, and scraping occurs along the outer diameter 3520 of the borehole resulting from the blade cutting action.

Referring now to FIGS. 37-39, another embodiment of a hybrid drill bit according to the present disclosure is shown. The bit 3700 has a bit body 3701 with a longitudinal axis 3702 extending through the bit, wherein the bit radius measured from a gage 3704 of the bit to the longitudinal axis 3702. At least one blade 3710 protrudes from the bit body, wherein the blade extends an axial distance along the gage 3704 of the bit body and a radial inward distance from the gage towards the longitudinal axis 3702. A plurality of blade cutting elements 3712 are disposed on the blades 3710, wherein the blade cutting elements comprise a blade cutting profile.

A plurality of journals 3720 extend downwardly from the bit body 3701. A roller cone 3730 is rotatably mounted to each of the journals 3720, and a plurality of roller cone cutting elements 3735 are disposed on each roller cone 3730, wherein the roller cone cutting elements comprise a roller cone cutting profile. The roller cones 3730 may be rotatably retained to the journals 3720 using a ball bearing system, wherein ball bearings may be inserted through a ball hole 3722 and into a race formed between the journal 3720 and roller cone 3730. Further, a lubrication passage 3724 may extend from a grease reservoir to the ball hole 3722 to provide lubrication to the ball bearing system. The blades 3710 extend to and along the gage 3704 of the bit 3700, while the roller cones 3730 extend to a position radially inward from the gage 3704.

Referring now to FIG. 13, another embodiment of a hybrid drill bit according to the present disclosure is shown. The bit 130 has a plurality of roller cones 131 and a plurality of blades 132 disposed on the cutting face 133 of the bit 130. Each of the roller cones 131 has a plurality of roller cone cutting elements 134 disposed in circumferential rows. Each of the blades 132 has a plurality of blade cutting elements 135 disposed at the leading face (i.e., the side of the blade that faces in the direction of bit rotation) of the blade 132. As shown, a portion of at least one blade 132 shares a radial position on the bit cutting face 133 with a portion of at least one roller cone 131. For example, a radial position 136 on the bit cutting face 133 is represented by a dashed line set a distance 137 from the longitudinal axis 138 of the bit 130. A portion of each blade 132 and each roller cone 131 overlaps with the radial position 136.

Further, the bit 130 shown in FIG. 13 has three blades 132 and three roller cones 131 disposed in an alternating arrangement around the bit cutting face 133. However, in other embodiments, a bit may have more or less blades and/or roller cones. For example, as shown in FIGS. 6 and 14, a hybrid drill bit 140 has six blades 144 and three roller cones 143 disposed on a bit body 141. Each roller cone 143 is rotatably mounted to a journal 150. Blades and roller cones in hybrid bits of the present disclosure may be in an alternating arrangement or other pattern. For example, a hybrid bit according to embodiments of the present disclosure may have four blades and two roller cones, wherein the blades and roller cones may be arranged in a pattern having each roller cone positioned between a pair of blades. FIGS. 21 and 22 show a bottom view and a side view, respectively, of a hybrid bit 2200 having four blades 2230 and two roller cones 2220, wherein each roller cone 2220 is positioned between a pair of blades 2230. FIG. 23 shows a bottom view of a hybrid bit 2300 according to embodiments of the present disclosure having six blades 2330, 2332 and two roller cones 2320, wherein each roller cone 2320 is positioned between a pair of blades 2330 and the remaining two blades 2332 are each positioned radially adjacent to each roller cone 2320.

As shown in FIGS. 14 and 6, the plurality of roller cones 143 are rotatably mounted to journals 150 extending from the bit face of the bit 140. The roller cones 143 extend a radial distance from a longitudinal axis 142 of the bit 140 to a distance radially inward from the gage of the bit. A plurality of blades 144 extend radially from the bit body 141 and axially along the bit body from a first end 145 to a second end 146, wherein the first end 145 is at a second radial distance from the longitudinal axis 142. Further, a radial position 147 on the bit cutting face is represented by a dashed line set a distance 148 from the longitudinal axis 142 of the bit 140. As shown, the roller cones 143 extend a radial distance from the longitudinal axis 142 to the farthest radial point of the roller cones that overlaps the radial position 147. A plurality of the blades 144 may also overlap the radial position 147, while some of the blades 149 do not overlap the radial position 147. In some embodiments, one or more blades may share a radial position with one or more roller cones, while at least one other blade may be radially farther than one or more roller cones. In some embodiments, each blade on a hybrid bit may be radially farther from the bit longitudinal axis than each roller cone, such that no blade shares a radial position with a roller cone. In other embodiments, each blade on a hybrid bit may share a radial position with each roller cone.

Referring now to FIG. 15, a hybrid bit 150 according to embodiments of the present disclosure is shown. The bit 150 has a longitudinal axis 151 extending there through and a plurality of blades 152 and a plurality of roller cones 153 disposed on the bit 150 a radial distance from the longitudinal axis 151. Each roller cone 153 is rotatably mounted to a journal (not shown) extending from the bit 150 cutting face. Each blade 152 extends axially along the bit body from a first end 154 to a second end 155, wherein the first end 154 is at a second radial distance from the longitudinal axis 151. As shown, the first end 154 of blades 152.1 are at a second radial distance from the longitudinal axis 151 that is less than the radially outermost point of the roller cones 153 (such that a portion of blades 152.1 radially overlap with a portion of the roller cones 153), and the first end of the remaining blades 152 are at a second radial distance from the longitudinal axis 151 that is greater than the radially outermost point of the roller cones 153. A plurality of roller cone cutting elements 156 are disposed on the roller cones 153, and a plurality of blade cutting elements 157 are disposed on the blades 152. As shown, the roller cone cutting elements 156 and blade cutting elements 157 have planar cutting surfaces. However, in some embodiments, such as shown in FIGS. 1 and 2, roller cone cutting elements may have non-planar cutting surfaces and blade cutting elements may have planar cutting surfaces. While not illustrated, it is also within the scope of the present disclosure that the blade cutting elements may be non-planar, such as those described, for example, in U.S. Patent Publication No. 2008/0035380.

Axial Positions

Radial positions of roller cone and blade cutting profiles may be designed based on the axial positions of the roller cone and blade cutting profiles. According to embodiments of the present disclosure, the blade cutting profile may axially overlap the roller cone cutting profile by up to 100 percent of the roller cone cutting profile. For example, as shown in FIG. 4, the blade cutting profile may extend an axial distance along the bit that axially overlaps with up to ¾ the axial distance of the roller cone cutting profile, and as shown in FIG. 5, the blade cutting profile may extend substantially to the same axial distance as the roller cone cutting profile to overlap with substantially the entire axial distance of the roller cone cutting profile. In some embodiments, the blade cutting profile may extend an axial distance past the axially lowest point of the roller cone cutting profile. Embodiments of the present disclosure may include roller cone cutting profiles and blade cutting profiles that are axially and radially positioned to axially and/or radially overlap. For example, a bit may have a blade cutting profile that axially overlaps the lowest axial point of the base of a journal, wherein the roller cone cutting profile radially overlaps the blade cutting profile by at least the radius of the first cutting element of the blade cutting profile.

According to embodiments of the present disclosure, a drill bit may include a bit body having a longitudinal axis extending there through, at least one blade extending from the bit body, a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements form a blade cutting profile, at least one journal extending downwardly from the bit body, a roller cone rotatably mounted to each of the at least one journals, and a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements form a roller cone cutting profile, and wherein the roller cone cutting profile extends an axial height greater than the blade cutting profile.

For example, referring again to FIG. 4, a cutting profile 400 of a hybrid drill bit includes a blade cutting profile 430 and a roller cone cutting profile 420, wherein the roller cone cutting profile 420 extends an axial height 450 greater than the blade cutting profile 430 (i.e., the roller cone cutting profile 420 extends axially lower than the blade cutting profile 430). The axial height 450 between the roller cone cutting profile 420 and the blade cutting profile 430 may range within the axial extent of the first row 422 of roller cone cutting elements. In some embodiments, the axial height 450 between the roller cone cutting profile 420 and the blade cutting profile 430 may range from greater than 0.1 inches (2.5 mm). For example, in some embodiments, the axial height between a roller cone cutting profile and a blade cutting profile may range from about 0 to about 3 inches (76.2 mm), or with a lower limit of any of 0.25 (6.35 mm), 0.5 (12.7 mm), 1.0 (25.4 mm), or 1.5 inches (38.1 mm), and an upper limit of any of 1.5 (38.1 mm), 2.0 (50.8 mm), 2.5 (63.5 mm), 2.75 (69.85 mm) or 3.0 inches (76.2 mm), where any lower limit can be used with any upper limit. In one or more embodiments, the blade cutting elements may have at least one axial overlap with at least one roller cone cutting element when that roller cone cutting element is rotated in an on-bottom position.

According to some embodiments of the present disclosure, a hybrid drill bit may include a bit body having a longitudinal axis extending there through, at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along a gage of the bit body and a radial inward distance from the gage towards the longitudinal axis, at least one journal extending downwardly from the bit body, wherein the at least one journal extends a length from a base of the journal, and a roller cone rotatably mounted to the at least one journal, wherein the lowest axial point of the at least one blade is axially lower than the lowest axial point of the base of the journal. In some embodiments having the lowest axial point of a blade that is axially lower than the lowest axial point of the base of the journal, the blade may axially overlap the lowest axial point of the base of the journal. In other embodiments having the lowest axial point of a blade that is axially lower than the lowest axial point of the base of the journal, the journal may be inset within the bit such that the blade does not axially overlap the lowest axial point of the base of the journal.

For example, FIG. 25 shows a cutting profile 2500 of a bit according to embodiments of the present disclosure. The bit has at least one journal 2510 extending downwardly and radially outward from a base 2512 at the bit body and a roller cone 2522 rotatably mounted to each journal 2510. Roller cone cutting elements mounted on the at least one roller cone 2522 form a roller cone cutting profile 2520 and blade cutting elements mounted on at least one blade form a blade cutting profile 2530. The blade cutting profile 2530 extends an axial distance along a gage 2532 (outer diameter) of the bit and a radial inward distance 2535 from the gage 2532 towards the longitudinal axis 2505, wherein the lowest axial point 2534 of the blade cutting profile 2530 is axially lower than the lowest axial point 2514 of the base 2512 of the journal 2510. As shown, the blades axially overlap the lowest axial point 2514 of the base 2512 of the journal 2510. Further, as shown, the lowermost axial point of the roller cone cutting profile 2520 extends axially lower than the lowermost axial point 2534 of the blade cutting profile 2530.

According to some embodiments of the present disclosure, a hybrid drill bit may have a plurality of blades and one journal extending from the bit body. For example, referring now to FIGS. 18-20, a bottom view, a side view and a partial profile view of a bit 180 may have one journal 190 extending from a bit cutting face 182 and a roller cone 184 rotatably mounted on the journal 190. The journal 190 has a journal axis 192 extending from the base 194 of the journal through the length of the journal 190. A plurality of blades 186 extend from the bit body 195 proximate the roller cone 184 radially and axially from the bit cutting face 182 along the bit body side face 181 (i.e., a substantially cylindrical region, as discussed above) through the bit gage. The bit cutting face 182 may have a curved transition to a circumferential side face 181. Particularly, each blade 186 extends from a first end 185 to a second end 187, wherein the first end 185 extends from the bit cutting face 182 and wherein the second end 187 extends from the side face 181 of the bit, along the bit gage. The roller cone 184 shares an axial position with at least one of the plurality of blades 186. In other words, the roller cone 184 and at least one of the blades 186 may intersect a radial plane at an axial position along the longitudinal axis of the bit 180. Further, in one or more embodiments, the journal 190 and at least one of the blades may each intersect a radial plane at an axial position along the longitudinal axis of the bit 180.

FIGS. 27 and 28 show cutting profiles of hybrid bits 2700, 2800 according to embodiments of the present disclosure having a plurality of blades and one journal extending from the bit body. As shown in FIG. 27, a bit 2700 may have one journal 2710 extending from a bit cutting face and a roller cone (not shown) rotatably mounted on the journal 2710. The journal 2710 has a journal axis 2712 extending from the base 2714 of the journal through the length of the journal 2710. A plurality of roller cone cutting elements 2720 disposed on the roller cone form a roller cone cutting profile and a plurality of blade cutting elements 2730 disposed on the plurality of blades form the blade cutting profile. The blade cutting elements 2730 form a blade cutting profile extending axially along the bit gage 2737 and a radial inward distance 2735 from the gage 2737 towards the longitudinal axis 2705. As shown, the blade cutting profile extends axially lower than the lowermost point 2716 of the journal base 2714 and radially inward to a position proximate to the roller cone cutting profile.

Referring now to FIG. 28, a bit 2800 has one journal 2810 extending from a bit cutting face and a roller cone (not shown) rotatably mounted on the journal 2810. The journal 2810 has a journal axis 2812 extending from the base 2814 of the journal through the length of the journal 2810. A plurality of roller cone cutting elements 2820 disposed on the roller cone form a roller cone cutting profile and a plurality of blade cutting elements 2830 disposed on the plurality of blades form the blade cutting profile. The blade cutting elements 2830 form a blade cutting profile extending axially along the bit gage 2837 and a radial inward distance 2835 from the gage 2837 towards the longitudinal axis 2805. As shown, the blade cutting profile extends axially lower than the lowermost point 2816 of the journal base 2814 and radially overlaps with the roller cone cutting profile.

According to some embodiments of the present disclosure, the axial position of one or more journals and roller cones mounted thereon may be inset from the axial position of one or more blades, such that the lowermost axial position of the blade cutting profile extends axially lower than the lowermost axial position of the roller cone cutting profile. In such embodiments, the blade cutting profile may axially overlap with 100% of the roller cone cutting profile. As used herein, the terms “lowermost” or “downward” refers to a direction facing away from the connection end of a bit and towards the bit cutting face.

For example, FIGS. 29-31 show a bottom view, schematic view, and perspective view of a hybrid bit according to embodiments of the present disclosure having a roller cone inset from the axial position of the blades. The bit 2900 has a bit body 2902 with a longitudinal axis 2904 extending axially there through. Further, the bit 2900 has a bit cutting face 2906 that engages a bottom side of a wellbore and a gage region 2908 that maintains the outer diameter of the wellbore. Bit 2900 includes a journal 2910 extending downwardly and radially outward from the bit 2900, a roller cone 2920 mounted to the journal 2910, and a plurality of blades 2930 (though other embodiments may include one or more roller cones and/or one or more blades) arranged in such a manner that the roller cone 2920 is inset from the blades 2930. A plurality of roller cone cutting elements 2925 is disposed on the roller cone 2920, and a plurality of blade cutting elements 2935 is disposed on the blades 2930. In the embodiment shown, the roller cone 2920 is inset a distance from the blades 2930 such that the lowest axial point of a blade is axially lower than the lowest axial point of the base of the journal, and the blades do not axially overlap the lowest axial point of the base of the journal. As shown, the lowermost axial point of the blades extend lower than the lowermost axial point of the roller cone cutting elements 2925, the lowermost axial point of the roller cone 2920 and the lowermost axial point of the journal 2910. However, in some embodiments, the lowermost axial point of the blades may extend lower than the lowermost axial points of the roller cone and journal, while the lowermost axial point of the roller cone cutting elements may extend lower than the lowermost axial point of the blades. In other embodiments, the lowermost axial point of the blades may extend lower than the lowermost axial point of the journal, while the lowermost axial points of the roller cone and the roller cone cutting elements may extend lower than the lowermost axial point of the blades.

According to embodiments of the present disclosure, a bit may have a cone diameter to blade radial span ratio ranging from ½ to 20/1, wherein the cone diameter is measured at the largest width along the cone axis and the blade radial span is measured from the gage of the bit to the radially most inward point of the blade. For example, in some embodiments, the cone diameter to blade radial span ratio may range from about ⅘ to 4/1. In another embodiment, such as in a relatively large diameter bit, the bit may have at least one blade and at least one roller cone, wherein the blade has a radial span supporting one cutting element and the bit has a cone diameter to blade radial span ratio ranging between 18/1 and 20/1. In another embodiment, a bit may have a cone diameter to blade radial span ratio ranging from about to 1/1. For example, a bit may have a relatively large diameter, such as ranging from 24 to 26 inches, one roller cone (e.g., with a roller cone diameter of about 5 to 6 inches) and at least one blade (e.g., having a blade radial span of about 10 to 12 inches), wherein the cone diameter to blade radial span ratio is about ½.

In some embodiments, more than one roller cone may be inset among a plurality of blades. The inset distance may be measured between the lowermost axial point of the roller cone cutting profile and the lowermost axial point of the blade cutting profile, and may depend on, for example, the size of the roller cone in relation to the blades and the size of the bit. According to embodiments of the present disclosure, a bit may have an inset distance ranging from a lower limit of 0 to an upper limit of the diameter of the bit. In some embodiments, the inset distance may range from greater than 0 to about 2 inches. Further, in embodiments having one or more roller cones inset among a plurality of blades, the roller cone cutting profile may radially overlap with the blade cutting profile, such as described above, or other embodiments, the roller cone cutting profile may be radially adjacent or radially apart from the blade cutting profile. In embodiments having one or more roller cones inset from a plurality of blades, wherein the roller cone cutting profile radially overlaps the blade cutting profile, the one or more roller cones may be assembled to the bit by, for example, screwing or otherwise attaching one or more journals to face downward and radially outward from the bit and rotatably mounting a roller cone to each journal. By designing the bit to have downward and radially outward facing journals (and thus mounted roller cones), whether the roller cones are inset from a plurality of blades or whether the roller cones extend axially lower than a plurality of blades, the bit may have improved cutting performance, as described more below.

Bit Performance Testing

Referring now to FIGS. 7-12 simulations of a bit known in the art having outwardly facing roller cones extending to the gage of the bit (and no blades) and a hybrid drill bit according to embodiments of the present disclosure were conducted to compare drilling performance Particularly, FIGS. 7 and 8 show a model of a bit 700 known in the art and a model of a hybrid bit 800 according to embodiments of the present disclosure, and FIGS. 9 and 10 show the cutting patterns 900, 100 in a borehole simulated from the bits 700, 800. Particularly, FIG. 9 shows the cutting pattern 900 of the bit having the outwardly facing roller cones shown in FIG. 7, and FIG. 10 shows the cutting pattern 100 of the hybrid bid of the present disclosure shown in FIG. 8. FIGS. 11 and 12 show graphs of the results of the simulation. In the simulations, cutting action was simulated for each bit 700, 800 such that a weight on the bit (“WOB”) of 18 klbs. (8,164 kg) was applied to the roller cones 750, 850 of each bit.

As shown in FIG. 11, a graph comparing the rate of penetration (“ROP”) of each of the bits 700, 800 modeled in FIGS. 7 and 8 shows that the ROP of the modeled hybrid bit according to the present disclosure was higher than the modeled bit having the outwardly facing roller cones. Particularly, the modeled bit having the outwardly facing roller cones extending to gage had a ROP of 63.71 ft/hr (19.42 m/hr), and the ROP of the modeled hybrid bit was 66.6 ft/hr (20.3 m/hr). FIG. 12 shows a graph comparing the scraping distance in relation to the cutting element placement on the bit. As used herein, “scraping distance” refers to a measurement of the distance of the cutting element shear/grinding on the formation per bit revolution. Scraping distance is also related to ROP and how much wear the cutting element experiences.

For conventional roller cone bits, cutting elements perform gouging/indentation action with less scraping distance than cutting elements of a bit having the outwardly facing roller cones, which has predominant shearing, or “high shear”, interaction with rock formations. High shear cutting action may provide higher ROP, but too much shear cutting action may cause premature wearing. Further, in conventional roller cone bits, increasing roller cone offset may increase scraping distance of cutting elements. However, bits having the outwardly facing roller cones may have higher scraping distance than a conventional roller cone bit, where the cutting elements of the conventional roller cone bit mainly do gouging and indentation. For example, a bit having the outwardly facing roller cones may have an average scraping distance of 0.5″ (12.7 mm), as shown in FIG. 12 and a conventional roller cone bit may have about 0.2-0.3″ (5.1-7.6 mm) scraping distance (not shown), except for cutting elements at the bit gage (outer cutting diameter), which often may have more than 0.5″ (12.7 mm) scraping distance. Higher scraping distance may provide increased shearing action in the bit and therefore more ROP. However, a first row of cutting elements of a conventional bit may have a scraping distance more than 1.5″ (38.1 mm), which may be too large and cause premature cutting element wear. On the other hand, because of the overlapped cutting element profiles in bits according to some embodiments of the present disclosure, the scraping distance of a first row of cutting elements may be reduced to 0.5 inches (12.7 mm). In this way, each of the cutting elements of roller cones in hybrid bits of the present disclosure may have a larger but uniform scraping distance, which may maintain the high shear ROP advantage but avoid the preferential wear of the bit having the outwardly facing roller cones.

For example, FIGS. 11 and 12 show that in similar ROP ranges, a hybrid bit of the present disclosure may maintain the advantage of high ROP and high steerability of a bit having the outwardly facing roller cones and also avoid the preferential wear of a bit having the outwardly facing roller cones. Particularly, FIGS. 11 and 12 show the scraping distance of each row of cutting elements plotted in relation to the radial distance of each row of cutting elements from the bit gage. The row of cutting elements closest to the gage in the bit 700 shown in FIG. 7 may have a higher scraping distance than the other rows of cutting elements, while each row of cutting elements in the modeled hybrid bit 800 according to one or more embodiments of the present disclosure scrapes relatively similar amounts of formation.

Referring now to FIGS. 40-44, comparisons of drilling simulations 4000, 4100, 4200, 4300 and 4400 for various types of drill bits are shown. Particularly, FIG. 40 shows the cutting action performed by a bit having roller cones facing downward and radially inward from a bit body, wherein the roller cones cut along the bottom face of the borehole to the outer diameter of the borehole. FIG. 41 shows the cutting action performed by a bit having roller cones facing downward and radially outward from a bit body, wherein the roller cones cut along the bottom face of the borehole to the outer diameter of the borehole. FIGS. 42 and 43 show the cutting action performed by bits according to embodiments of the present disclosure having blades that cut along the bottom face and outer diameter of the borehole and roller cones facing downward and radially outward that cut along a portion of the bottom face of the borehole. The bit simulated in FIG. 43 has a larger radial overlapping region between the roller cones and blades than the bit simulated in FIG. 42. Particularly, the radial overlap region of the bit of FIG. 42 is about 1.35 inches, while the radial overlap region of the bit of FIG. 43 is about 1.75 inches, and the bit diameter for both bits in FIGS. 42 and 43 is about 8.75 inches. FIG. 44 shows the cutting action performed by a bit having blades that cut along the bottom face and outer diameter of the borehole.

FIGS. 45 and 46 show graph comparisons for the resulting cutting performance from the simulations shown in FIGS. 40-44. Particularly, FIG. 45 shows the rate of penetration (ROP) of the bits and FIG. 46 shows the torque of the bits, where simulations were conducted with a 20 klb weight on bit at 120 revolutions per minute (RPM). As shown, the bit simulated in FIG. 43 with a relatively larger overlapping region of blade and roller cone cutting action results in a greater rate of penetration and torque than bits having relatively smaller overlapping blade and roller cone cutting action and bits without blade cutting action.

A hybrid drill bit according to various embodiments of the present disclosure may be formed from steel. Specifically, a bit body may be formed of steel having 0.15-0.35% carbon by weight, and from 0.15-0.2% carbon by weight (such as used to form roller cone bits) or 0.25-0.35% carbon by weight (such as used to form fixed cutter bits) in particular embodiments. Bit bodies formed from steel may have journals integral with the bit body (i.e., formed together), which are machined into the desired shape and position on the bit body, and blades separately attached to the bit body. In some embodiments, a bit body formed of steel may have blades integral with the bit body and journals separately attached thereto. Further, blades and journals may both be integral with a steel bit body, or, blades and journals may both be separately attached to the steel bit body. Use of separately attached blades and/or journals may be desired due to different material requirements for each component, based on their structure, function, manufacturing details, expected loads, etc. For example, a bit body and blades may be formed together from steel, the bit body including a nozzle bore, a reservoir for lubricant or grease, cutter pockets, and journal assembly holes. In some embodiments, a hybrid drill bit may be formed of a matrix material, such as a carbide hard phase, e.g., one or more transition metal carbides such as tungsten carbide, disposed in binder phase, e.g., one or more metals selected from Group VIII of the Periodic Table. In embodiments having a roller cone body part made separately from the journals, the journals may be made of steel, such as 4815 or 8720 steel.

Upon forming the bit body having blades and journals extending therefrom, roller cones may be assembled to the journals using a ball or pin bearing retention system, such as described above. For example, in some embodiments, a plurality of bearing balls may be fitted into complementary ball races foamed in a journal and corresponding roller cone to retain the roller cone on the journal. These balls may be inserted through a ball passage, which extends through the bit body to the journal between the bearing races. The ball passage may transverse the bit body a total length that is greater than the length of the radius from a centerline or longitudinal axis of the bit to the opening in ball race. A roller cone may first be fitted on the journal, and then the bearing balls may be inserted through ball passage to fit in the space between ball races. Balls may be retained in the ball races by a ball retainer, which may be inserted into a passage after the balls, and then secured in place (such as by a plug welded in place). The balls may carry any thrust loads tending to remove the roller cone from the journal and thereby retain the roller cone on the journal. In some embodiments, the ball passages may intersect near the bit centerline; however, the intersection of the ball passages may depend on bit size, cone number, etc. Additionally, it is also within the scope of the present disclosure that the ball passages may extend approximately to a bit centerline. Such an embodiment may be used when manufacturing the bit from multiple pieces, such as described in U.S. Application Publication No. 2011/0023663.

According to embodiments of the present disclosure, hybrid bits may be designed to have radially and/or axially displaced roller cone and blade cutting profiles. By radially displacing a blade cutting profile from a roller cone cutting profile in a hybrid drill bit according to embodiments of the present disclosure, high inner cutting efficiency may be provided by the high shear feature of the outwardly facing roller cones, increased steerability may be provided with some rotating cutting elements contacting the wall of the wellbore, and a wider range of formation drilling may be achieved.

Although only a few example embodiments have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the example embodiments without materially departing from this invention. Accordingly, all such modifications are intended to be included within the scope of this disclosure as defined in the following claims. 

What is claimed is:
 1. A drill bit, comprising: a bit body having a longitudinal axis extending there through; a plurality of journals extending downward and radially outward from the bit body, each journal having a journal axis extending from a base of the journal through the length of the journal, wherein the journal axis at the base is at a first radial distance from the longitudinal axis; a roller cone rotatably mounted to each of the journals; and at least one blade protruding from the bit body and extending axially and radially along the bit body from a first end to a second end, wherein the first end is at a second radial distance from the longitudinal axis greater than the first radial distance, and wherein the second end is at a gage region of the drill bit.
 2. The drill bit of claim 1, wherein the first radial distance ranges from greater than 0 to ½ of the bit radius.
 3. The drill bit of claim 1, further comprising a center cutting element disposed on the bit body substantially at the longitudinal axis.
 4. The drill bit of claim 1, wherein a radial distance from the bit longitudinal axis to the radially outermost point of one of the at least one journals extends radially past the first end of the at least one blade.
 5. The drill bit of claim 1, wherein the axially lowermost point of the at least one blade extends lower than the axially lowermost point of the roller cone.
 6. A drill bit, comprising: a bit body having a longitudinal axis extending there through; a bit radius measured from a gage of the bit to the longitudinal axis; at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along the gage of the bit body and a radial inward distance from the gage towards the longitudinal axis; a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements comprise a blade cutting profile; a plurality of journals extending downwardly from the bit body; a roller cone rotatably mounted to each of the journals; and a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements comprise a roller cone cutting profile, and wherein the roller cone cutting profile radially extends from a first end to a second end located radially inward from the gage.
 7. The drill bit of claim 6, wherein the radial inward distance of the at least one blade ranges from ⅓ to ¾ of the bit radius.
 8. The drill bit of claim 6, wherein the roller cone cutting profile is radially adjacent to the blade cutting profile.
 9. The drill bit of claim 6, wherein the roller cone cutting profile extends an axial height greater than the blade cutting profile.
 10. The drill bit of claim 6, wherein the roller cone cutting profile radially overlaps with at least the radius of a first blade cutting element on the blade cutting profile.
 11. The drill bit of claim 10, wherein the roller cone cutting profile radially overlaps with the blade cutting profile a distance less than or equal to ½. of the bit radius.
 12. The drill bit of claim 10, wherein the blade cutting profile radially overlaps the roller cone cutting profile up to the entire radial length of the roller cone cutting profile.
 13. The drill bit of claim 6, wherein the roller cone cutting profile extends an axial height less than the blade cutting profile.
 14. The drill bit of claim 6, further comprising a center cutting element disposed substantially at the longitudinal axis.
 15. The drill bit of claim 6, wherein the roller cone comprises an extension length to diameter ratio ranging from greater than 0.5.
 16. A drill bit, comprising: a bit body having a longitudinal axis extending there through; at least one blade protruding from the bit body, wherein the at least one blade extends an axial distance along a gage of the bit body and a radial inward distance from the gage towards the longitudinal axis; at least one journal extending downwardly from the bit body, wherein the at least one journal extends a length from a base of the journal; and a roller cone rotatably mounted to the at least one journal; wherein the lowest axial point of the at least one blade is axially lower than the lowest axial point of the base of the journal.
 17. The drill bit of claim 16, wherein the drill bit comprises one journal.
 18. The drill bit of claim 16, further comprising: a plurality of blade cutting elements disposed on the at least one blade, wherein the blade cutting elements comprise a blade cutting profile; and a plurality of roller cone cutting elements disposed on each roller cone, wherein the roller cone cutting elements comprise a roller cone cutting profile; wherein the blade cutting profile axially overlaps the roller cone cutting profile by up to 100 percent of the roller cone cutting profile.
 19. The drill bit of claim 18, wherein the blade cutting profile extends an axial distance lower the axially lowest point of the roller cone cutting profile.
 20. The drill bit of claim 18, wherein the drill bit comprises two or more journals, and wherein the journals face radially outward. 